1. Field of the Invention
The present invention relates generally to modem on hold. More particularly, the present invention relates to using in-band signaling to facilitate modem on hold.
2. Background
The widespread use of the Internet as a daily research, entertainment, and communication tool has increased the deployment of modems and other communication devices. Many homes and offices use their existing telephone lines to access the Internet via modems. The existing lines, however, may support some subscriber-selected features, such as a call-waiting feature, which may interrupt a modem connection. Other similar interruptions may occur while using modems or other communication systems.
Recently, various modem-on-hold schemes have been suggested to remedy such interruptions. For example, when a call-waiting interrupts a communication session established between a local modem and remote modem, the local modem receiving the call-waiting interruption may request an on-hold period from the remote modem, so that the call waiting may be answered. In order to act upon or respond to a call waiting event, local modem may need to communicate with its data terminal equipment (“DTE”), such as a host software running on a personal computer or data circuit equipment (“DCE”). Typically, such communications between the DTE and the DCE are achieved using various predetermined command sets, such as the well-known AT commands. For the local modem or the DCE to accept commands from the DTE, conventionally, the local modem must be placed in command mode, so that the DCE does not transmit the data received from the DTE to the remote modem, but treat such data as commands.
One conventional scheme to cause the local modem to escape to command mode is through use of an escape sequence that can be detected by the local modem during data transfer. One such escape sequence includes transmission of three predetermined characters, such as “+++”, from the DTE to the local modem, provided that no data is transmitted from the DTE to the local modem for one second prior to transmission of the three characters, that the three characters are transmitted within a one-second period, and that no more data is transmitted after the last character for a one-second period. If all such criteria are detected and confirmed by the local modem to have been met, the local modem responds with an “OK” message indicating to the DTE that the local modem can accept commands from the DTE. However, while in command mode, either the data being received from the remote modem will be discarded or the local modem will utilize flow control to request the remote modem to cease data transmission while the local modem is in command mode. Once the DTE is ready to exit command mode and return to data mode, the DTE may issue a command known as ATO to request the local modem to return to data mode.
Such schemes, however, introduce many drawbacks when used in conjunction to place modem communications on hold. One drawback is that the local modem is not permitted to switch out of data mode unless requested by the DTE; therefore, the local modem can only inform the DTE of a call waiting event through hardware means, for example by a hardware signal. Further, even after the local modem informs the DTE of the call waiting event through hardware means, the DTE must at that point transmit the escape sequence to enter command mode if the DTE wishes to interrogate the local modem for caller ID information and alike. However, as explained above, not only the escape sequence could take more than three seconds to be transmitted and detected, even yet, once the local modem escapes to command mode, data communication with the remote modem is interrupted. As a result, the user must face data interruption even though the user may not be interested in answering the call waiting.
Accordingly, there is an intense need in the art for systems and method that can communicate a modem-on-hold event to the DTE more efficiently and without interruption of the data flow between the local modem and the remote modem. Furthermore, there is a need in the art for systems and methods that can provide a user-transparent modem-on-hold communications between the local modem and the DTE.